Life on Earth: the highlights – Part 3

In parts 1 and 2 I looked at the key events in the history of life, from the birth of the Earth up to the evolution of the dinosaurs.

In part three I’ll continue from the dinosaurs right up to the appearance of humanity, and its finest work, Ellen Page.

As with the previous posts I’ll give approximate times for each event millions of years and I’ll use the label Ma for millions (mega-annum). I’ll also show the time in terms of a 24-hour clock. The last event I looked at was 225 million years ago, or 22:49 on the 24-hour clock. The next event is…

The first mammal scurries out of its burrow; (210 Ma) 22:54 – many people assume that mammals appeared after the dinosaurs had died out, but actually they evolved shortly after the dinosaurs. The first mammals were small (a few cm), warm-blooded, nocturnal, covered in fur and probably ate insects. Early examples include Morganucodon watsoni. Mammals remained small and nocturnal for many millions of years, likely hiding from the dominant dinosaurs in their burrows.

The first flowers bloom; (130 Ma) 23:19 – although the Earth had been thickly vegetated since the late Devonian period (around 380 Ma), none of the plants from before this moment had flowers, reproducing instead with spores and seeds. Flowers may seem merely a pleasant decoration, but as flowers evolved the pollination relationship with insects also emerged, and this is one of the key features of plant-life on our Earth today; many of the crops we depend upon are at least partly dependent on insect pollination, including coffee.

The dinosaurs, and many other species, are wiped out in the K-T extinction event; (65 Ma) 23:39 – this is the most famous of the big five extinction events, the one that involved an asteroid or comet striking Chicxulub in Mexico and saw the end of the dinosaurs, as well as many other groups of animals, including the large marine reptiles, flying reptiles and ammonites. Scientists are still debating whether the impact was the sole cause, as evidence suggests the dinosaurs were waning before the impact, and many took thousands of years to go extinct after the collision. Other causes of extinction have also been implicated, such as a flood basalt eruption. Either way, the removal of the dinosaurs freed many ecological niches, which were exploited primarily by birds and mammals, prompting a burst in the evolution of both.

The first grass sprouts; (40 Ma) 23:47 – this may sound like an odd evolutionary innovation to mention, but grass has played an important role in the evolution of many species we are familiar with today. Many of the most famous mammals eat grass, from bison to cows, or live primarily in grasslands, like lions. In fact, the spread of grasslands may have triggered some ape species to leave the trees and begin walking on two legs. Sound familiar?

The first apes’ swing into action; (22 Ma) 23:53 – apes are a type of primate; they have two legs, two arms, no tail and include animals like chimpanzees, gorillas and humans. The fossil record suggests apes first evolved in Africa, and quickly diversified into a broad range of species, much more diverse than the variety of apes’ existing today. Apes’ may have been so successful as they were likely intelligent and adaptable animals, capable of solving problems and forming relatively complex social groups.

The first homo stride over the Earth; (2.5 Ma) 23:59 – homo are the group of apes that we belong to, it means man. The earliest homo we’re aware of is Homo habilis, and there have been many different species of human, including Homo erectus and Homo neanderthalensis. Contrary to popular belief, humans’ didn’t evolve in a straight line leading up to our species. The true human tree of life is more like a bush, with lots of different lineages, with one branch leading to us, but other branches ending in extinction. Unfortunately we’re the only human species left.

The first Homo sapiens look up at the sky; (0.2 Ma) 23:59:56 – that’s us, Homo sapiens means ‘wise man’, some might say a pretty poor choice of name. Many people know modern humans evolved relatively recently, but not many people appreciate just how recently, we’ve only been around for 4 seconds in terms of the 24 hours the Earth has existed. Homo sapiens chief achievement has been our technology, and the pace of its advancement has increased exponentially, from language, to agriculture, to industrial society, to science, right up to the internet. Our future technological advances seem boundless and some have predicted that we will spread throughout the stars.

Homo sapiens invents the radio; (1895) 23:59:59998 – this may sound like an odd invention for me to single-out, but radiowaves are a great form of communication for talking throughout the Universe. If we are going to communicate with extraterrestrial civilizations on different planets then radio would be a great way to do this. Radiowaves are actually a type of light (a type of light we can’t see though), and light is one of the few things in nature that can travel large distances at great speeds. The Universe is full of different types of light, but relatively little in the spectrum of radiowaves, so radio looks like a great choice. Also, many astrobiologists define extraterrestrials as intelligent at the point they invent radio technology. This would mean that the Earth produced its first intelligent species in the last few ten thousands of a second of its existence.

A quick disclaimer. Throughout these posts I’ve missed out a lot of events in the history of life, including some of the big mass-extinctions and evolutionary innovations; I did this because I wanted the post to be short and not overly complex. If you think I missed out something particularly fun, then please comment. Also, I’ve presented lots of the events in a very simplified manner and sometimes with a bit more certainty than they deserved, as many events are heavily debated. A great example is the Snowball Earth events; where scientists are currently debating the extent to which the Earth froze, how many times, and the effect on life. I’ve done this as I wanted to present the history of life as an interesting narrative and I didn’t want to go into too much detail for each event. If you don’t agree with something I’ve written then I’m happy to have a (good natured) argument in the comments section.

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